Air circuit breakers as described within U.S. Pat. No. 3,095,489 entitled "Manual Charging Means for Stored Energy Closing Mechanisms of Electric Circuit Breakers" and U.S. Pat. No. 3,084,238 entitled "Ratchet Mechanism for Charging a Closing Spring in an Electric Circuit Breaker" include operating mechanisms that are mainly exposed to the environment. Since the air circuit breakers are rated to carry several thousand amperes of current continuously, the exposure to convection cooling air assists in keeping the operating components within reasonable temperature limits.
Such air circuit breakers are usually provided with a motor operator such as described in U.S. Pat. No. 4,167,988 entitled "Ratcheting Mechanism for Circuit Breaker Motor Operator" or a manual handle as described in U.S. Pat. No. 3,729,065 entitled "Means for Charging A Stored Energy Circuit Breaker Closing Device" for charging the powerful closing springs contained within the air circuit breaker operating mechanism.
When the circuit breaker closing springs are brought to their fully-charged conditions, it is important that the springs do not become inadvertently discharged while an operator has hold of the charging handle in order to avoid damage to the ratchet mechanism and the associated air circuit breaker contacts. An early arrangement of a latching means to prevent rotation of a closing springs charging handle is found in U.S. Pat. No. 4,475,021 entitled "Air Circuit Breaker".
The above-noted U.S. patents include means for opening and closing the circuit breaker contacts by direct access to the circuit breaker as well as from a remote location. To prevent closing the circuit breaker contacts when the associated electric equipment is undergoing replacement or repair, interlocks are required. U.S. Pat. No. 5,504,285 entitled "Circuit Breaker Indicating Flag Interlock Arrangement Operating Springs" and U.S. Pat. No. 5,478,979 entitled "Circuit Breaker Closing and Opening Interlock Assembly" provide interlock arrangements acting between the circuit breaker ON and OFF buttons to prevent inadvertent turn on of so-called "insulated case" circuit breakers wherein the circuit breaker operating components are completely contained within a common enclosure. U.S. patent application Ser. No. 08/878,594 entitled "Pushbutton Interlock Mechanism for an Industrial Rated Circuit Breaker" (filed concurrently herewith) describes a recent interlock approach that interacts with the circuit breaker indicating assembly to provide the interlock function.
It is known that circuit breaker contacts can become welded closed upon repeated intense overcurrent occurrence, especially when the circuit breaker is used within circuits that occasionally carry circuit current in excess of the circuit breaker ratings.
When multipole circuit breakers such as described in the aforementioned U.S. Pat. Nos. 3,084,238 and 3,905,489 incur one set of welded contacts while the remainder of the contacts within the separate poles remain operational, it is essential to provide indication that one of the contacts has become welded.
When higher ampere rated circuit breakers that employ a pair of arcing contacts along with a pair of main contacts operate off a common contact carrier, the arcing contacts close before the main contacts and open after the main contacts to protect the main contacts from arc deterioration. However, if either of the pair of arcing and main contacts become welded, the contact indicating assembly could indicate that the contacts are in the OFF condition since the other pair of the main or arcing contacts has separated.
This problem also arises when the circuit breaker includes three or more poles and main as well as arcing contacts are employed within each pole. The forces provided by the contact opening springs could overcome the holding forces exerted on the contact carrier, that is common to each pole, by the welded contacts and motivate the indicating assembly into the OFF condition are involved.
One purpose of the invention, accordingly, is to prevent the contact indicating assembly from providing indication of open contacts when at least one pair of the circuit breaker contacts are welded in the ON condition and the remaining contacts have moved to the OFF condition.